U.S. patent application number 16/237770 was filed with the patent office on 2019-07-11 for inspection method and inspection apparatus.
This patent application is currently assigned to NuFlare Technology, Inc.. The applicant listed for this patent is NuFlare Technology, Inc.. Invention is credited to Hideaki Hashimoto, Ryoichi Hirano, Riki Ogawa, Masataka Shiratsuchi, Hideo Tsuchiya.
Application Number | 20190213726 16/237770 |
Document ID | / |
Family ID | 67159944 |
Filed Date | 2019-07-11 |
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United States Patent
Application |
20190213726 |
Kind Code |
A1 |
Hirano; Ryoichi ; et
al. |
July 11, 2019 |
INSPECTION METHOD AND INSPECTION APPARATUS
Abstract
There is provided an inspection method including acquiring an
inspection image by irradiating a sample with a plurality of
electron beams and by simultaneously scanning the sample by the
electron beams, performing first correction of a reference image
corresponding to the inspection image or second correction of the
inspection image based on a plurality of distortions of each of the
electron beams and on a position scanned by each of the electron
beams in the inspection image, and performing first comparison of
the reference image subjected to the first correction with the
inspection image or second comparison of the reference image with
the inspection image subjected to the second correction.
Inventors: |
Hirano; Ryoichi;
(Setagaya-ku, JP) ; Tsuchiya; Hideo; (Setagaya-ku,
JP) ; Shiratsuchi; Masataka; (Kawasaki-shi, JP)
; Hashimoto; Hideaki; (Yokohama-shi, JP) ; Ogawa;
Riki; (Kawasaki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NuFlare Technology, Inc. |
Yokohama-shi |
|
JP |
|
|
Assignee: |
NuFlare Technology, Inc.
Yokohama-shi
JP
|
Family ID: |
67159944 |
Appl. No.: |
16/237770 |
Filed: |
January 2, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03F 7/7065 20130101;
G01N 2223/6116 20130101; G06T 2207/30148 20130101; G06T 7/001
20130101; G01N 23/2251 20130101; G01N 21/8851 20130101; G01N
21/95607 20130101 |
International
Class: |
G06T 7/00 20060101
G06T007/00; G01N 21/956 20060101 G01N021/956; G01N 21/88 20060101
G01N021/88; G03F 7/20 20060101 G03F007/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 11, 2018 |
JP |
2018-002386 |
Claims
1. An inspection method comprising: acquiring an inspection image
by irradiating a sample with a plurality of electron beams and by
simultaneously scanning the sample by the electron beams;
performing first correction of a reference image corresponding to
the inspection image or second correction of the inspection image
based on a plurality of distortions of each of the electron beams
and on a position scanned by each of the electron beams in the
inspection image; and performing first comparison of the reference
image subjected to the first correction with the inspection image
or second comparison of the reference image with the inspection
image subjected to the second correction.
2. The inspection method according to claim 1, wherein the position
is obtained based on coordinates of a sample table on which the
sample is placed.
3. The inspection method according to claim 1, wherein the
distortions are a distortion relating to a position, a distortion
of beam brightness, a distortion of beam shape, or a distortion of
beam blur.
4. An inspection method comprising: performing first acquisition of
a reference image by irradiating a first area having a first
pattern of a sample with a plurality of electron beams and by
simultaneously scanning the first area by the electron beams;
performing second acquisition of an inspection image by irradiating
a second area having a second pattern of the sample with the
electron beams such that a same pattern portion of the second
pattern as the first pattern is irradiated with a same electron
beam among the electron beams and by simultaneously scanning the
second area by the electron beams; and comparing the reference
image with the inspection image.
5. The inspection method according to claim 4, further comprising:
performing the second acquisition of the inspection image such that
the same pattern portion of the second pattern as the first pattern
is irradiated with the same electron beam among the electron beams
based on coordinates of a sample table on which the sample is
placed.
6. The inspection method according to claim 4, further comprising:
performing first correction of the reference image and second
correction of the inspection image based on a plurality of
distortions of each of the electron beams, on a position scanned by
each of the electron beams in the reference image, and on a
position scanned by each of the electron beams in the inspection
image.
7. The inspection method according to claim 6, wherein the
distortions are a distortion relating to a position, a distortion
of beam brightness, a distortion of beam shape, or a distortion of
beam blur.
8. An inspection apparatus comprising: an image acquisition circuit
configured to perform first acquisition of a reference image by
irradiating a first area having a first pattern of a sample with a
plurality of electron beams and by simultaneously scanning the
first area by the electron beams, and to perform second acquisition
of an inspection image by irradiating a second area having a second
pattern of the sample with the electron beams such that a same
pattern portion of the second pattern as the first pattern is
irradiated with a same electron beam among the electron beams and
by simultaneously scanning the second area by the electron beams;
and a comparator circuit configured to compare the reference image
with the inspection image.
9. The inspection apparatus according to claim 8, further
comprising: an image pattern determination circuit configured to
find the same pattern portion of the second pattern as the first
pattern by comparing the reference image with the inspection image
and to confirm whether the same pattern portion of the reference
image and the same pattern portion of the inspection image are
irradiated with the same electron beam among the electron
beams.
10. The inspection apparatus according to claim 8, wherein the
image acquisition circuit performs the second acquisition of the
inspection image such that the same pattern portion of the second
pattern as the first pattern is irradiated with the same electron
beam among the electron beams based on coordinates of a sample
table on which the sample is placed.
11. The inspection apparatus according to claim 8, further
comprising: an image correction circuit configured to perform first
correction of the reference image and second correction of the
inspection image based on a plurality of distortions of each of the
electron beams, on a position scanned by each of the electron beams
in the reference image, and on a position scanned by each of the
electron beams in the inspection image.
12. The inspection apparatus according to claim 11, wherein the
distortions are a distortion relating to a position, a distortion
of beam brightness, a distortion of beam shape, or a distortion of
beam blur.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority from Japanese Patent Applications No. 2018-002386, filed
on Jan. 11, 2018, the entire contents of which are incorporated
herein by reference.
FIELD OF THE INVENTION
[0002] Embodiments described herein relate generally to an
inspection method and an inspection apparatus.
BACKGROUND OF THE INVENTION
[0003] In recent years, as large-scale integrated circuits (LSI)
are highly integrated and have large capacity, the circuit line
width required for semiconductor elements has been getting
narrower. These semiconductor elements are manufactured using an
original image pattern on which a circuit pattern is formed (also
referred to as a mask or a reticle, and, hereinafter, collectively
referred to as a mask) by exposing and transferring a pattern onto
a wafer with a reduction projection exposure apparatus called a
stepper to form a circuit.
[0004] For manufacturing LSIs requiring large manufacturing costs,
it is indispensable to improve yield. However, as represented by
1-gigabit class random access memories (DRAM), patterns
constituting LSIs are on the order of submicron to nanometer. In
recent years, as the LSI pattern dimension formed on a
semiconductor wafer is miniaturized, the dimension to be detected
as a pattern defect has been extremely small. Thus, the accuracy of
an inspection apparatus that inspects a defect of an
ultraminiaturized pattern transferred onto a semiconductor wafer is
required to be improved. Besides, one of the major factors for
lowering the yield is a pattern defect of a mask used when an
ultraminiaturized pattern is exposed and transferred onto a
semiconductor wafer by a photolithography technique. Thus, the
accuracy of an inspection apparatus that inspects a defect of a
transfer mask used for manufacturing LSIs is required to be
improved.
[0005] There is a known method, as an inspection method, for
performing inspection by comparing an optical image obtained by
imaging a pattern formed on a sample, such as a wafer including a
semiconductor wafer or a mask including a lithography mask, at a
predetermined magnification using an enlarging optical system with
design data or an optical image obtained by imaging the same
pattern of the sample. For example, an inspection method includes a
"die-to-die inspection" in which the comparison of optical image
data obtained by imaging the same pattern at different positions on
the same mask is performed, and a "die-to-database inspection" in
which drawing data (design pattern data) obtained by converting
pattern-designed CAD data into a device input format for a drawing
apparatus to perform input when a pattern is drawn on a mask is
input to an inspection apparatus, design image data (reference
image) is generated based on the drawing data, and the design image
data is compared with an optical image, which is measurement data,
obtained by imaging the pattern. In the inspection method in the
inspection apparatus, a substrate to be inspected is placed on a
stage (sample table), and a light flux scans the sample as the
stage moves to perform inspection. The substrate to be inspected is
irradiated with a light flux by a light source and an illumination
optical system. Light having transmitted through or reflected from
the substrate to be inspected is imaged on a sensor via the optical
system. The image imaged by the sensor is transmitted as
measurement data to a comparator circuit. After the images are
aligned with each other, the comparator circuit compares the
measurement data with reference data in accordance with an
appropriate algorithm and determines that there is a pattern defect
when they do not match.
[0006] The above inspection apparatus acquires an optical image by
irradiating a substrate to be inspected with a laser beam and
imaging its transmission image or reflection image. On the other
hand, an inspection apparatus that irradiates a substrate to be
inspected with a multi-beam constituted by a plurality of electron
beams in an array arrangement, in which beams arrayed at the same
pitch on a straight line are aligned in rows, and detects secondary
electrons corresponding to the respective beams emitted from the
substrate to be inspected to obtain a pattern image has been
developed. The inspection apparatus using electron beams including
a multi-beams scans each small area of a substrate to be inspected
to detect secondary electrons.
SUMMARY OF THE INVENTION
[0007] An inspection method in an aspect of the present disclosure
includes acquiring an inspection image by irradiating a sample with
a plurality of electron beams and by simultaneously scanning the
sample by the electron beams, performing first correction of a
reference image corresponding to the inspection image or second
correction of the inspection image based on a plurality of
distortions of each of the electron beams and on a position scanned
by each of the electron beams in the inspection image, and
performing first comparison of the reference image subjected to the
first correction with the inspection image or second comparison of
the reference image with the inspection image subjected to the
second correction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a configuration diagram showing a configuration of
an inspection apparatus according to a first embodiment;
[0009] FIG. 2 is a schematic diagram showing a configuration of a
shaping aperture array member according to the first
embodiment;
[0010] FIG. 3 is a view for explaining a path of a beam in the
inspection apparatus according to the first embodiment;
[0011] FIGS. 4A to 4C are schematic diagrams showing a method for
acquiring an inspection image of a pattern on a wafer according to
the first embodiment;
[0012] FIG. 5 is a schematic diagram showing how a beam scan area
(inspection image acquisition area) is irradiated with a plurality
of electron beams according to the first embodiment;
[0013] FIGS. 6A and 6B are schematic diagrams of inspection images
acquired under the influence of a distortion relating to a position
of each electron beam in the beam scan area (inspection image
acquisition area) according to the first embodiment;
[0014] FIG. 7 is a flowchart of the first embodiment;
[0015] FIG. 8 is a schematic diagram for explaining the outline of
an inspection method according to a second embodiment; and
[0016] FIG. 9 is a flowchart of the second embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Hereinafter, embodiments of the present disclosure are
described with reference to the drawings.
First Embodiment
[0018] An inspection method of the present embodiment includes
acquiring an inspection image by irradiating a sample with a
plurality of electron beams and by simultaneously scanning the
sample by the electron beams, performing first correction of a
reference image corresponding to the inspection image or second
correction of the inspection image based on a plurality of
distortions of each of the electron beams and on a position scanned
by each of the electron beams in the inspection image, and
performing first comparison of the reference image subjected to the
first correction with the inspection image or second comparison of
the reference image with the inspection image subjected to the
second correction.
[0019] An inspection apparatus in the present embodiment includes
an image acquisition mechanism that acquires an inspection image
which is a secondary electron image of a sample by irradiating the
sample with a plurality of electron beams and by simultaneously
scanning the sample by the electron beams, and an image storage
unit that stores the inspection image and a position scanned by
each of the electron beams in the inspection image, a distortion
storage unit that stores a plurality of distortions of each of the
electron beams, an image correction circuit that performs first
correction of a reference image corresponding to the inspection
image or second correction of the inspection image based on the
distortions and the position, and a comparator circuit that
performs first comparison of the reference image subjected to the
first correction with the inspection image or second comparison of
the reference image with the inspection image subjected to the
second correction.
[0020] FIG. 1 is a configuration diagram showing a configuration of
an inspection apparatus according to the present embodiment. In
FIG. 1, an inspection apparatus 100 that inspects a pattern formed
on a substrate is an example of a charged-particle beam inspection
apparatus. An electron beam is an example of a charged particle
beam. The inspection apparatus 100 includes an electro-optical
image acquisition mechanism (image acquisition mechanism, image
acquisition circuit) 150 and a control system circuit 160 (control
unit). The electro-optical image acquisition mechanism 150 includes
an electron beam column 102 (electron lens barrel), an examination
chamber 103, a detection circuit 106, a stripe pattern memory 123,
a stage drive mechanism 142, and a laser measuring machine 122. In
the electron beam column 102, an electron gun 201, an illumination
lens 202, a shaping aperture array substrate 203, a reduction lens
205, a limiting aperture substrate 206, an objective lens 207, a
main deflector 208, a sub deflector 209, a collective blanking
deflector 212, a beam separator 214, projection lenses 224 and 226,
a deflector 228, and a multi-detector 222 are disposed.
[0021] In the examination chamber 103, an XY stage (sample table)
105 movable at least on an XY plane is disposed. On the XY stage
105, a substrate (sample) 101 on which a chip pattern to be
inspected is formed is disposed. The substrate 101 includes a
semiconductor substrate such as an exposure mask or a silicon
wafer. The substrate 101 is disposed on the XY stage 105 with, for
example, a pattern forming surface facing upward. On the XY stage
105, a mirror 216 that reflects a laser beam for measuring the
length of a laser emitted from the laser measuring machine 122
disposed outside the examination chamber 103 is disposed. The
multi-detector 222 is connected to the detection circuit 106
outside the electron beam column 102. The detection circuit 106 is
connected to the stripe pattern memory 123.
[0022] In the control system circuit 160, a control computer 110,
which is a computer, is connected to, via a bus 120, a position
circuit 107, a comparator circuit 108, a generation circuit 111, a
reference circuit 112, a stage control circuit 114, a lens control
circuit 124, a blanking control circuit 126, a deflection control
circuit 128, a distortion storage unit 130, an image storage unit
132, an image correction circuit 134, an image pattern
determination circuit 136, a pattern data storage unit 109 such as
a magnetic disk device, a monitor 117, a memory 118, and a printer
119. The stripe pattern memory 123 is connected to the comparator
circuit 108. The XY stage 105 is driven by the drive mechanism 142
under the control of the stage control circuit 114. In the drive
mechanism 142, for example, a drive system, such as a three-axis
(X-Y-.theta.) motor driven in the X direction, the Y direction, and
the .theta. direction, is configured, and the XY stage 105 is
movable. For example, step motors can be used for these X motors, Y
motors, and .theta. motors (not shown). The XY stage 105 is movable
in the horizontal direction and the rotation direction by motors of
X, Y, and .theta. axes. The moving position of the XY stage 105 is
measured by the laser measuring machine 122 and supplied to the
position circuit 107. The laser measuring machine 122 receives the
reflected light from the mirror 216 to measure the position of the
XY stage 105 by the principle of the laser interference method.
[0023] The electron gun 201 is connected to a high voltage power
supply circuit (not shown), and emits, as an electron beam,
electron groups emitted from the cathode and accelerated by
application of an acceleration voltage between a filament (not
shown) and an extraction electrode (not shown) in the electron gun
201 from the high voltage power supply circuit and by application
of a predetermined voltage of the extraction electrode and heating
of a predetermined temperature to the cathode (filament). For
example, electromagnetic lenses are used for the illumination lens
202, the reduction lens 205, the objective lens 207, and the
projection lenses 224 and 226, and are controlled by the lens
control circuit 124. The beam separator 214 is also controlled by
the lens control circuit 124. The collective blanking deflector 212
and the deflector 228 each are constituted by electrode groups of
at least two poles and are controlled by the blanking control
circuit 126. The main deflector 208 and the sub deflector 209 each
are constituted by electrode groups of at least four poles and are
controlled by the deflection control circuit 128.
[0024] When the substrate 101 is a semiconductor wafer on which a
plurality of chip (die) patterns is formed, pattern data of the
chip (die) patterns is input from the outside of the inspection
apparatus 100 and stored in the pattern data storage unit 109. When
the substrate 101 is an exposure mask, design pattern data, which
is a basis for forming a mask pattern on the exposure mask, is
input from the outside of the inspection apparatus 100 and stored
in the pattern data storage unit 109.
[0025] Here, FIG. 1 shows the constituent elements necessary for
explaining the first embodiment. The inspection apparatus 100 may
have other necessary constituent elements in general.
[0026] FIG. 2 is a schematic diagram showing a configuration of a
shaping aperture array member according to the first embodiment. In
FIG. 2, the shaping aperture array substrate 203 is provided with
two-dimensional (matrix) N (X direction).times.N' (Y direction)
holes (openings) 22 formed at a predetermined arrangement pitch L
in the X and Y directions, where N is an integer of 2 or more, N'
is an integer of 1 or more, the X direction is the horizontal
direction to be referred to as a first direction, and the y
direction is the vertical direction to be referred to as a second
direction. When the reduction magnification of the multi-beam is
"a" (when the multi-beam diameter is reduced to 1/a to irradiate
the substrate 101), and the pitch between multi-beams in the X and
Y directions on the substrate 101 is set to "p", the arrangement
pitch L is L=(a.times.p). In the example of FIG. 2, the holes 22
for forming N=5.times.N'=5 (5.times.5) multi-beams are formed.
Next, the movement of the electro-optical image acquisition
mechanism 150 in the inspection apparatus 100 is described.
[0027] FIG. 3 is a view for explaining a path of a beam in the
inspection apparatus according to the first embodiment. An electron
beam 200 emitted from the electron gun 201 (emission source)
substantially vertically illuminates the entire shaping aperture
array substrate 203 by the illumination lens 202. As shown in FIG.
2, a plurality of rectangular holes 22 (openings) are formed in the
shaping aperture array substrate 203, and the electron beam 200
illuminates an area including all of the holes 22. A part of the
electron beam 200 with which the position of each of the holes 22
is irradiated passes through each of the holes 22 of the shaping
aperture array substrate 203, and a plurality of, for example,
rectangular or circular shaped electron beams (multi-beams) (a
plurality of electron beams) 20a to 20d (solid lines in FIGS. 1 and
3) are formed.
[0028] Then, the formed multi-beams 20a to 20d form crossovers
(C.O.), pass through the beam separator 214 disposed at a crossover
position of the multi-beams 20, are reduced by the reduction lens
205, and travel toward the center hole formed in the limiting
aperture substrate 206. Here, when the whole of the multi-beams 20a
to 20d are collectively deflected by the collective blanking
deflector 212 disposed between the shaping aperture array substrate
203 and the reduction lens 205, the multi-beams 20a to 20d are
deviated from the position of the center hole of the limiting
aperture substrate 206, and are shielded by the limiting aperture
substrate 206. On the other hand, the multi-beams 20a to 20d not
deflected by the collective blanking deflector 212 pass through the
center hole of the limiting aperture substrate 206 as shown in FIG.
1. Blanking control is performed by turning on/off the collective
blanking deflector 212, and beam ON/OFF is collectively controlled.
In this manner, the limiting aperture substrate 206 shields the
multi-beams 20a to 20d deflected by the collective blanking
deflector 212 so as to be in the beam OFF state. The multi-beams
20a to 20d are formed with the groups of beams formed from the beam
ON state until the beam OFF state and having passed through the
limiting aperture substrate 206. The multi-beams 20a to 20d having
passed through the limiting aperture substrate 206 are focused by
the objective lens 207 to be a pattern image (beam diameter) with a
desired reduction ratio. Then, the whole of the multi-beams 20a to
20d having passed through the limiting aperture substrate 206 are
collectively deflected by the main deflector 208 and the sub
deflector 209 in the same direction to irradiate the corresponding
irradiation position of each beam on the substrate 101. At this
time, the whole of the multi-beams 20 are collectively deflected by
the main deflector 208 so as to irradiate respective reference
positions of unit inspection areas to be scanned by each beam,
which are to be described later, and tracking deflection is also
performed to follow the movement of the XY stage 105. Then, the
whole of the multi-beams 20 are collectively deflected by the sub
deflector 209 so that the beams scan corresponding N.times.N'
sub-areas (grids 29 to be described later) in the unit inspection
area. Ideally, the multi-beams 20 to be emitted at a time are
arranged at a pitch obtained by multiplying the arrangement pitch L
(=ap) of the holes 22 of the shaping aperture array substrate 203
by the above desired reduction ratio (1/a). In this manner, the
electron beam column 102 irradiates the substrate 101 with the
two-dimensional N.times.N' multi-beams 20 at a time. A bundle of
secondary electrons (multi secondary electrons 300) corresponding
to each of the multi-beams 20 is emitted from the substrate 101
(see dotted lines in FIGS. 1 and 3) due to the irradiation of
desired positions on the substrate 101 with the multi-beams 20.
[0029] The multi secondary electrons 300 emitted from the substrate
101 are refracted to the center side of the multi secondary
electrons 300 by the objective lens 207 and travel toward the
center hole formed in the limiting aperture substrate 206. The
multi secondary electrons 300 having passed through the limiting
aperture substrate 206 are refracted in the direction substantially
parallel to the optical axis by the reduction lens 205 and travel
to the beam separator 214.
[0030] Here, the beam separator 214 generates an electric field and
a magnetic field in directions orthogonal to each other on a plane
orthogonal to the traveling direction (optical axis) of the
multi-beams 20. The electric field exerts a force in the same
direction regardless of the traveling direction of electrons. In
contrast, the magnetic field exerts a force in accordance with the
Fleming's left-hand rule. Thus, it is possible to change the
direction of the force acting on electrons depending on the
entering direction of electrons. The force from the electric field
and the force from the magnetic field cancel each other in the
multi-beams 20 (primary electron beam) entering the beam separator
214 from the upper side, and the multi-beams 20 travel straight
downward. On the other hand, the force from the electric field and
the force from the magnetic field both work in the same direction
in the multi secondary electrons 300 entering the beam separator
214 from the lower side, and the multi secondary electrons 300 are
bent obliquely upward.
[0031] The multi secondary electrons 300 bent obliquely upward are
refracted by the projection lenses 224 and 226, and projected onto
the multi-detector 222. The multi-detector 222 detects the
projected multi secondary electrons 300. The multi-detector 222
includes a diode type two-dimensional sensor (not shown). Then, at
the position of the diode-type two-dimensional sensor corresponding
to each of the multi-beams 20, each secondary electron of the multi
secondary electrons 300 collides with the diode-type
two-dimensional sensor and generates electrons, and secondary
electron image data is generated for each pixel to be described
later. When the multi-detector 222 does not detect the multi
secondary electrons 300, the multi secondary electrons 300 are
blanking-deflected by the deflector 228 so that the multi secondary
electrons 300 do not reach the light receiving surface.
[0032] FIGS. 4A to 4C are schematic diagrams showing a method for
acquiring an inspection image of a pattern on a wafer according to
the present embodiment.
[0033] FIG. 4A is a schematic diagram showing that a plurality of
shots S is formed on a wafer W. In each of the shots S, a pattern
to be inspected by the inspection apparatus 100 is formed. Each of
the shots S is formed by one exposure using, for example, a mask,
but may be formed by a plurality of exposures.
[0034] FIG. 4B is a schematic diagram showing how an inspection die
D is scanned by the multi-beams 20. FIG. 4B shows an inspection end
area Z, an inspection stripe U, a beam scan area (inspection image
acquisition area) T, and an inspection start area R.
[0035] FIG. 4C is a schematic diagram showing the movement of the
wafer W in the inspection stripe U. The inspection stripe U (wafer
W) is moved so as to cross the beam scan area T.
[0036] FIG. 5 is a schematic diagram showing how the beam scan area
T (inspection image acquisition area) is irradiated with a
plurality of electron beams (multi-beams 20) according to the
present embodiment. It is assumed that the holes 22 for forming
nine (3.times.3) multi-beams are formed in the shaping aperture
array substrate 203 (FIG. 2).
[0037] In order to inspect a pattern, the inspection die D to be
inspected is scanned by the multi-beams 20. The beam scan area
(inspection image acquisition area) T in the inspection die D is
irradiated with the multi-beams 20. At this time, the wafer W is
moved in, for example, a direction opposite to the X direction so
as to cross the beam scan area T (see FIG. 4C). By moving the
multi-beams 20 in the Y direction and in the direction opposite to
the Y direction together with the movement of the wafer W, the
entire beam scan area T is scanned to acquire an inspection image
of the beam scan area T.
[0038] The above operation is performed to acquire an inspection
image in the inspection stripe U. When the inspection in the
inspection stripe U is completed, the wafer W is moved in the Y
direction by the length of the inspection stripe U in the Y
direction, and the wafer W is moved in the X direction to further
acquire the inspection image. This continues until the beam scan
area T crosses the inspection end area from the inspection start
area to acquire the entire inspection image in the inspection die
D.
[0039] FIG. 4B shows that the size of the inspection die D is equal
to the size of the shot S, but, for example, a plurality of
inspection dies D may be formed in the shot S.
[0040] FIGS. 6A and 6B are schematic diagrams of inspection images
acquired under the influence of a distortion relating to the
position of each of the electron beams in the beam scan area T
according to the present embodiment.
[0041] FIG. 6A is a schematic diagram showing how an area (scan
area) to be scanned by each of the electron beams is changed under
the influence of a distortion relating to the position of each of
the electron beams.
[0042] There is optical aberration in the optical system through
which the electron beams pass. Due to this optical aberration, each
of the electron beams has a distortion. An example of the
distortion is a distortion relating to a position. The distortion
relating to a position is that a position on the wafer W which is
deviated from the design is irradiated with an electron beam.
Although the scan area indicated by the solid line in FIG. 6A is
designed to be scanned, the area indicated by the dotted line is
scanned due to the distortion relating to a position.
[0043] FIG. 6B is a schematic diagram of an inspection image
acquired under the influence of the distortion relating to the
position of each electron beam. Although the inspection image
corresponding to the scan area indicated by the solid line is
designed to be acquired, the image indicated by the dotted line is
acquired due to the distortion relating to the position. For
example, when an area A' having a rectangular shape elongate in the
X direction as shown in FIG. 6A is scanned by the electron beam
corresponding to an area A, the corresponding inspection image is
acquired as an image A'' having a shape in which a square is
distorted to be elongate in the Y direction. When an area B' which
is larger in both the X direction and the Y direction than the
design as shown in FIG. 6A is scanned by the electron beam
corresponding to an area B, the corresponding inspection image is
acquired as an image B'' which is smaller in both the X direction
and the Y direction than the design.
[0044] Furthermore, due to the distortion relating to the position,
a defect to be detected by the electron beam corresponding to a
specific area can be detected by a different electron beam.
[0045] Distortions of electron beams include a distortion of beam
brightness, a distortion of beam shape, and a distortion of beam
blur. The distortion of beam brightness means, for example, that
the brightness of each electron beam is different. If defects are
the same size, the defects will be detected to be smaller when
detected with a dark electron beam than with a bright electron
beam.
[0046] The distortion of beam shape means, for example, that the
shape of an electron beam on the surface of the wafer W is a circle
whereas the shape of another electron beam is elliptical.
[0047] The distortion of beam blur means that a specific electron
beam is focused on the surface of the wafer W, whereas another
electron beam is not focused on the surface of the wafer W.
[0048] FIG. 7 is a flowchart of an inspection method according to
the present embodiment.
[0049] First, a wafer W to be inspected (substrate 101) on which a
pattern is formed is placed on the XY stage 105 (S12).
[0050] Next, the beam scan area T of the wafer W is irradiated with
the multi-beams 20 constituted by a plurality of electron beams
(S14).
[0051] While the beam scan area T is being irradiated with the
multi-beams 20, the XY stage 105 is moved so that the inspection
stripe U of the wafer W passes through the beam scan area T (S16),
and an inspection image is acquired (S18). The acquired inspection
image is stored in, for example, the image storage unit 132.
[0052] "The position scanned by each of the electron beams in the
inspection image" is described with reference to FIG. 5 as an
example. In FIG. 5, inspection images of an area 1, an area 2, an
area 3, an area 4, an area 5, an area 6, an area 7, an area 8, and
an area 9 are acquired using nine multi-beams in total. "The
position scanned by each of the electron beams in the inspection
image" means which area of the inspection image is acquired by
which electron beam among the electron beams. "The position scanned
by each of the electron beams in the inspection image" is also
stored in the image storage unit 132 together with the acquired
inspection image.
[0053] Next, a reference image is acquired (S20). The pattern data
for creating the reference image is stored in the pattern data
storage unit 109. Thus, the control computer 110 reads the pattern
data from the pattern data storage unit 109, generates the pattern
data using the generation circuit 111, and creates the reference
image using the reference circuit 112. The reference image acquired
in this manner is stored in, for example, the image storage unit
132.
[0054] Next, using the image correction circuit 134, the control
computer 110 performs first correction of the reference image
corresponding to the inspection image or second correction of the
inspection image, based on a plurality of distortions of each of
the electron beams and the position scanned by each of the electron
beams in the inspection image (S22). The distortions of each of the
electron beams are measured in advance and stored in the distortion
storage unit 130.
[0055] Next, the control computer 110 performs, using the
comparator circuit 108, first comparison of the reference image
subjected to the first correction with the inspection image, or
second comparison of the reference image with the inspection image
subjected to the second correction (S24).
[0056] Next, the effects of the present embodiment are
described.
[0057] As a semiconductor pattern is miniaturized, there is a
demand for an inspection apparatus and an inspection method capable
of simultaneously scanning an area with a plurality of electron
beams having high inspection resolution disposed in a matrix, and
of simultaneously acquiring an inspection image having a plurality
of patterns.
[0058] Here, each of the electron beams has distortions such as a
distortion relating to a position, a distortion of beam brightness,
a distortion of beam shape, and a distortion of beam blur. Thus,
the acquired inspection image is changed due to the distortions. On
the other hand, in a reference image created from pattern data, the
image is not assumed to be changed due to such distortions of
electron beams. For this reason, the distortions of electron beams
cause a problem in inspecting and comparing the inspection image
and the reference image.
[0059] According to the inspection method in the present
embodiment, it is possible to correct the reference image or the
inspection image based on which portion of the inspection image is
acquired by which electron beam and on the distortions of electron
beams. Accordingly, it is possible to provide an inspection method
capable of suppressing erroneous detection of defects.
[0060] By calculating the positions, in the inspection image, of
the electron beams used for the acquisition based on the
coordinates of the stage on which the sample is placed, it is
possible to associate the electron beams used for the acquisition
with the inspection image.
[0061] According to the inspection method in the present
embodiment, it is possible to provide an inspection method capable
of suppressing erroneous detection of defects.
Second Embodiment
[0062] An inspection method in the present embodiment includes
performing first acquisition of a reference image by irradiating a
first area having a first pattern of a sample with a plurality of
electron beams and by simultaneously scanning the first area by the
electron beams, performing second acquisition of an inspection
image by irradiating a second area having a second pattern of the
sample with the electron beams such that a same pattern portion of
the second pattern as the first pattern is irradiated with a same
electron beam among the electron beams and by simultaneously
scanning the second area by the electron beams, and comparing the
reference image with the inspection image.
[0063] An inspection apparatus in the present embodiment includes
image acquisition mechanism that performs first acquisition of a
reference image by irradiating a first area having a first pattern
of a sample with a plurality of electron beams and by
simultaneously scanning the first area by the electron beams, and
performs second acquisition of an inspection image by irradiating a
second area having a second pattern of the sample with the electron
beams such that a same pattern portion of the second pattern as the
first pattern is irradiated with a same electron beam among the
electron beams and by simultaneously scanning the second area by
the electron beams, and a comparator circuit that compares the
reference image with the inspection image.
[0064] The description overlapping with the first embodiment is
omitted.
[0065] The inspection method in the present embodiment is a
die-to-die inspection method.
[0066] FIG. 8 is a schematic diagram for explaining the outline of
the inspection method in the present embodiment.
[0067] The inspection method in the present embodiment is a
die-to-die inspection method. Thus, a reference image is acquired
by irradiating a reference die (first area) with a plurality of
electron beams. In addition, an inspection image is acquired by
irradiating an inspection die (second area) with a plurality of
electron beams. Then, by comparing the reference image with the
inspection image, inspection is performed.
[0068] Here, in order to perform the comparison, it is necessary
that the same pattern is included in the reference image and the
inspection image. In addition, in order to eliminate the influence
of distortions of electron beams, it is preferable that the same
pattern is scanned by the same electron beam. Thus, the same
pattern portion of the inspection die as the pattern of the
reference die is to be irradiated with the same electron beam.
[0069] FIG. 9 is a flowchart of the inspection method in the
present embodiment.
[0070] After (S16), first acquisition of a reference image is
performed by irradiating a first area having a first pattern of a
sample with a plurality of electron beams and by simultaneously
scanning the first area by the electron beams (S40). The reference
image and the position scanned by each of the electron beams in the
reference image are stored in an image storage unit 132.
[0071] Next, second acquisition of an inspection image is performed
by irradiating a second area having a second pattern with a
plurality of electron beams so that the same pattern portion of the
second pattern as the first pattern is irradiated with the same
electron beam among the electron beams and by simultaneously
scanning the second area by the electron beams (S42). The
inspection image and the position scanned by each of the electron
beams in the inspection image are stored in the image storage unit
132.
[0072] Here, the second acquisition of the inspection image may be
performed so that the same pattern portion of the second pattern as
the first pattern is irradiated with the same electron beams among
the electron beams based on the coordinates of a stage on which the
sample is placed.
[0073] An image pattern determination circuit 136 is used to
irradiate the same pattern portion of the second pattern as in the
first pattern with the same electron beam among the electron beams.
The image pattern determination circuit 136 finds the same pattern
portion by, for example, comparing the reference image with the
inspection image. Next, the image pattern determination circuit 136
confirms whether the same pattern portion of the reference image
and the same pattern portion of the inspection image are irradiated
with the same electron beam. The function of the image pattern
determination circuit 136 is not limited to this.
[0074] Note that, the second acquisition of the inspection image
may be performed first, and, then, the first acquisition of the
reference image may be performed.
[0075] Next, the reference image is compared with the inspection
image (S44).
[0076] Before the reference image is compared with the inspection
image, an image correction circuit 134 may perform first correction
of the reference image and second correction of the inspection
image based on the position scanned by each of the electron beams
in the reference image and the position scanned by each of the
electron beams in the inspection image.
[0077] Next, the effects of the present embodiment are
described.
[0078] In a die-to-die inspection, it is possible to provide an
inspection method capable of suppressing false detection of defects
by performing inspection taking distortions of electron beams into
account.
[0079] In the die-to-die inspection, by irradiating the same
pattern portion with the same electron beam, it is possible to
easily perform inspection without correction due to distortions
unlike a die-to-database inspection.
[0080] On the other hand, since the same pattern portions in the
reference image and in the inspection image are compared in the
die-to-die inspection, the image pattern determination circuit 136
is used to compare the same pattern portions irradiated with the
same electron beam among a plurality of electron beams between the
inspection image and the reference image. Accordingly, it is
possible to provide an inspection method capable of suppressing
false detection of defects in the die-to-die inspection.
[0081] Naturally, it is possible to perform a more accurate
inspection in the die-to-die inspection by correcting distortions
of electron beams. In particular, by correcting the distortion of
beam brightness, it is possible to easily compare the sizes of
defects included in the inspection image acquired with each
electron beam.
[0082] In the above description, a series of "mechanisms" or
"circuits" includes a processing circuit, and the processing
circuit includes an electric circuit, a computer, a processor, a
circuit board, a quantum circuit, a semiconductor device, or the
like. In addition, "circuits" may be a common processing circuit
(same processing circuit). Alternatively, "circuits" may be
different processing circuits (separate processing circuits). A
program for executing a processor or the like may be recorded in a
recording medium such as a magnetic disk device, a magnetic tape
device, an FD, or a read only memory (ROM). In addition, "recording
units", "storage units" or recording devices include a recording
medium such as a magnetic disk device, a magnetic tape device, an
FD, a read only memory (ROM), or a solid state drive (SSD).
[0083] The embodiments of the present disclosure have been
described with reference to specific examples. The above
embodiments are merely described as examples, and do not limit the
present disclosure. In addition, the constituent elements of each
embodiment may be appropriately combined.
[0084] For example, the inspection of a pattern formed on a wafer W
has been described as an example in the embodiments, but the
inspection of a pattern formed on a mask can also be preferably
described.
[0085] In the embodiments, the descriptions which are not directly
necessary for the explanation of the present disclosure, such as
the configurations of the inspection method and the inspection
apparatus, and its manufacturing method, are omitted, but the
configuration of the necessary inspection method can be
appropriately selected and used. In addition, all inspection
methods that include the elements of the present disclosure and can
be appropriately designed and changed by those skilled in the art
are included in the scope of the present disclosure. The scope of
the present disclosure is defined by the scope of the claims and
their equivalents.
* * * * *